1. Field of the Invention
The present invention relates to a cleaning machine for a printer cylinder such as a blanket cylinder of an offset printer and a plate cylinder of a gravure printer by pressing a cleaning cloth onto an outer peripheral surface of the cylinder by means of a pressure pad, and more particularly, to a long service life pressure pad for a cleaning machine of a printer.
2. Description of the Prior Art
The following explanation will be made as to a blanket cylinder cleaning machine for an offset printer but a gravure printer cylinder may be cleaned in the same way.
An offset printer usually has three cylinders, namely, a plate cylinder, a blanket cylinder and an impression cylinder. These cylinders are arranged such that their axes extend in parallel with one another and such that they can be brought into mutual contact. A sheet-like blanket made of rubber or the like is wound over an outer peripheral surface of a blanket cylinder of a printer. A pair of a cleaning cloth supply roll and a cleaning cloth take-up roll are rotatably supported in parallel to a longitudinal axis of the blanket cylinder on a pair of side plates mounted on both side frames of a printer body. A continuous cleaning cloth is wound at its both ends around the rolls by applying with a predetermined tension. The cleaning cloth take-up roll is driven to rotate at a predetermined speed by a drive means to take up the cleaning cloth thereon. A stay having a substantially T-shaped cross-section is provided to extend in parallel with an axial direction of the rolls with its ends being fixed to the side plates. A pressure pad made of elastic material such as rubber is provided in air-tight contact with a surface of the stay facing the blanket cylinder. A plenum chamber defined by the end of the stay and the pressure pad is in communication with an air compressor provided in the outside. When air is supplied to the plenum chamber, the pressure pad is inflated or expanded so that the cleaning cloth will be pressed against the outer peripheral surface of the blanket. During the pressure contact with the rotating blanket cylinder, contaminants on the blanket is wiped off by the cleaning cloth.
An another conventional cleaning machine of a printer has a pressure pad composed of a projected solid member made of rubber or the like. The pressure pad has a flange portion and a projected portion and is mounted through a holder on a mount member supported integrally with the side plate.
The projected portion of the pressure pad abuts against the cleaning cloth. The side plates are moved toward the blanket cylinder so that the cleaning cloth is pressed against the blanket thereby cleaning the blanket surface by the cleaning cloth.
In the foregoing coventional machines, the pressure pad is worn down or deformed due to friction against the cleaning cloth or is likely to be damaged due to a mechanical shock. Therefore, it is necessary to replace the pressure pad by new one normally after 10,000 to 20,000 times in use. Thus, the conventional techniques suffer from a disadvantage in which a durable service life of the pressure pad is relatively short.